Lexicon validations

[mary-ext]

Some thoughts at the top of my head as I figure out how to get a lexicon validator that works, especially one for my needs.

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1. Reduce the ambient module declarations to just the stuff necessary to get the typed HTTP client working, rename the module specifier to be something like @atcute/lexicons/http
2. Lexicon types should be imported from their respective packages, app.bsky.* lexicons should be imported from @atcute/bluesky, same goes for @atcute/whitewind and so on.
3. Move com.atproto.* lexicons to a separate @atcute/atproto package

Some of these aren't strictly necessary, but given that these type declarations and lexicon validations are pretty nifty for anyone using it outside of the typed HTTP client, I should at least accomodate for it for my next chance at revisiting this

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1. We could provide validateX and isX functions just like what @atproto/api is providing, however:

   • Only validateX provides a safe-parsing functionality
   • isX is used to check whether the object in question either has no $type field, or the field exists and matches the expected type for that object.

2. There's like 3 different ways to validate data, and they're all neat for their own cases.

   if (v.is(AppBskyFeedPost.Record, record)) {
     // handy if you just want to know if it's valid
   }
   
   // this one throws, handy for anything that requires the value to exactly match
   v.parse(AppBskyFeedPost.Record, record);
   
   // this one doesn't throw, if it returns `ok: false` you can deal with the error however you see fit
   v.safeParse(AppBskyFeedPost.Record, record);